28
Check Gas Input (Natural Gas Only)
To measure the gas input using the gas meter proceed
as follows:
1. Turn off gas supply to all other appliances except the
furnace.
2. With the furnace operating, time the smallest dial on
the meter for one complete revolution. If this is a 2
cubic foot dial, divide the seconds by 2; if it is a 1
cubic foot dial, use the seconds as is. This gives the
seconds per cubic foot of gas being delivered to the
furnace.
3. INPUT = GAS HTG VALUE x 3600 SEC. PER
CUBIC FOOT (3600 is a conversion factor - 3600
seconds = one hour)
Example: Natural gas with a heating value of 1000
BTU per cubic foot and 34 seconds per cubic foot
as determined by Step 2, then:
Input
= 1000 x 3600 ÷ 34
= 106,000 BTU per Hour
NOTE:
BTU content of the gas should be obtained
from the gas supplier.
This measured input must not be greater than the
input indicated on the rating plate of the furnace.
4. Relight all other appliances turned off in step 1
above. Be sure all pilot burners are operating.
Check Main Burner Flames
Flames should be stable, soft and blue, (dust may
cause
orange tips but they must not be yellow). They
should extend directly outward from the burner without
curling, floating or lifting off. (Fig. 32)
On GUD models, the flame may be inspected through
the observation window on the front cover of the burner
box.
Check the burner flames for:
1. Good adjustment
2. Stable, soft and blue
3. Not curling, floating, or lifting off.
Figure 32
Burner Flame
Check Temperature Rise
Check the temperature rise through the unit by placing
thermometers in supply and return air registers as close
to the furnace as possible. Thermometers must not be
able to see the furnaces heat exchangers, or false
readings could be obtained.
1. All registers must be open; all duct dampers must be
in their final (fully or partially open) position, and the
unit operated for 15 minutes before taking readings.
2. The temperature rise must be within the range speci-
fied on the rating plate.
NOTE:
Air temperature rise is the temperature differ-
ence between supply and return air.
With a properly designed system, the proper tempera-
ture rise will normally be obtained when the unit is
operated at rated input with the recommended blower
speed.
If the correct temperature rise is not obtained, it may be
necessary to change the blower speed. A higher blower
speed will decrease the temperature rise. A slower blower
speed will increase the temperature rise.
NOTE:
Blower speed must be set to give the correct air
temperature rise through the furnace as marked on the
rating plate.
Changing Blower Speeds
WARNING
To avoid electrical shock, injury or death,
when changing speed taps turn off power
to the furnace.
A multispeed motor is used in the furnace blower. It
provides easy speed selection for both heating and
cooling air flow. The Specification Sheet shows the
CFM and E.S.P. relationship for proper selection of
heating and cooling speeds. All furnaces ship as high
speed for cooling and the speed listed on the wiring
diagram for heating. These speeds should be adjusted
by the installer to match the local conditions.
Refer to the WIRING DIAGRAM on the furnace to
connect the correct motor leads to the correct control
terminals. If heating speed will equal cooling speed, use
the jumper wire provided. All unused motor leads that
are not connected to park terminals on the control
must be taped.
